Synthesis and characterization of Ag NPs templated via polymerization induced self-assembly

Accepted Manuscript Synthesis and characterization of Ag NPs templated via polymerization induced selfassembly Yaoming Zhang, Paulina Filipczak, Guping He, Grzegorz Nowaczyk, Lukasz Witczak, Wojciech Raj, Marcin Kozanecki, Krzysztof Matyjaszewski, Joanna Pietrasik PII:

S0032-3861(17)30920-5

DOI:

10.1016/j.polymer.2017.09.047

Reference:

JPOL 20016

To appear in:

Polymer

Received Date: 7 August 2017 Revised Date:

17 September 2017

Accepted Date: 21 September 2017

Please cite this article as: Zhang Y, Filipczak P, He G, Nowaczyk G, Witczak L, Raj W, Kozanecki M, Matyjaszewski K, Pietrasik J, Synthesis and characterization of Ag NPs templated via polymerization induced self-assembly, Polymer (2017), doi: 10.1016/j.polymer.2017.09.047. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Synthesis and characterization of Ag NPs templated via polymerization induced self-assembly

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Yaoming Zhang1, Paulina Filipczak2, Guping He3, Grzegorz Nowaczyk4, Lukasz Witczak1, ，2, 5

and Joanna Pietrasik*1

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Wojciech Raj1, Marcin Kozanecki2, Krzysztof Matyjaszewski*

1. Institute of Polymer and Dye Technology, Lodz University of Technology, Stefanowskiego 12/16, 90-924 Lodz, Poland

2. Department of Molecular Physics, Lodz University of Technology, Zeromskiego 116, 90-924 Lodz, Poland

Nottingham, UK

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3. School of Chemistry, University of Nottingham, University Park Nottingham NG7 2RD,

4. NanoBioMedical Centre at Adam Mickiewicz University in Poznan, Umultowska 85, PL

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61614 Poznań, Poland

5. Department of Chemistry, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh,

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Pennsylvania 15213, United States

KEYWORDS PISA; SERS; RAFT; nanoparticles; template; ABSTRACT Spherical poly(acrylic acid)-block-polystyrene (PAA-b-PS) nano-objects were prepared via polymerization induced self-assembly (PISA) and used as templates for the synthesis of silver nanoparticles (Ag NPs). The PAA shells on the spheres acted as templates for the formation of immobilized Ag NPs by loading Ag+ ions followed by reduction. The templates covered with discrete Ag NPs showed surface-enhanced Raman spectroscopy (SERS) effect as

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substrates for adenine detection and high catalytic activity for reduction of 4-nitrophenol to 4aminophenol.

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1. Introduction

Polymerization induced self-assembly (PISA) enables the block copolymers (BCPs) to organize in situ to generate well-defined nano-objects. Recently, this process has gained increasing attention as a new approach, alternative to the BCPs self-assembly in bulk. [1-5] In PISA

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process, the polymerization of a second block from a solvophilic chain gradually converts a soluble monomer to solvophobic polymer segment, rendering the self-assembly of synthesized

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block copolymer. The initially formed morphology in PISA-based systems are spherical micelles with the core and the corona-forming blocks. The increase of the molecular weight of the coreforming blocks results in nanostructure reorganization from spheres to wormlike, and then to vesicles or to higher order structures. [6-10] PISA has been explored as a useful tool to fabricate BCPs based nano-objects with various morphologies that can be easily tailored through

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numerous parameters.[10-14]

Due to well-defined morphology at the nanometer range, the self-assembled BCPs were successfully used as templates to generate functional nanomaterials by selective localization of metal or metal oxide precursors and the subsequent redox reaction.[15-20] A similar concept can

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be applied to PISA systems; however, only a few examples have been reported so far. For instance, it was reported that the PISA nano-objects with tunable morphologies can be decorated with 10 nm of iron oxide and gold nanoparticles (Au NPs) by complexation of the precursors

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with the solvophilic segment.[21, 22] A discrete, well-organized layer of gold NPs with size of 1 to 3 nm was created within the shell of PISA formed poly(4-vinylpyridine)-block-polystyrene spheres via the coordination of gold ions within pyridine segments.[23] The PISA formed cylinders were synthesized within silica nanotubes.[24] Also, the possibility of synthesis of 10 nm silver nanoparticles (Ag NPs) within PISA nano-objects was reported by reducing Ag+ ion complexed with core forming block ketoester.[25] However, the position of the nanoparticles on the polymer templates was not controlled.

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Herein, we explored the simple PISA system to prepare well-defined templates for the synthesis of well-aligned Ag NPs. Poly(acrylic acid)-block-polystyrene (PAA-b-PS), was synthesized by PISA and formed core-shell spheres, composed of a PS core and a PAA shell. Ag NPs were prepared from Ag+ ions localized at the shell via electrostatic interactions between the carboxylic

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acid groups of the PAA block and Ag+ ions, followed by reduction, nucleation and growth of the NPs. The Ag NPs were successfully used as efficient catalysts for the reduction of 4-nitrophenol to 4-aminophenol. The as-prepared materials were tested as a SERS substrate for adenine detection. This procedure offers a facile approach to tailor a versatile array of Ag NPs within

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PISA objects and could be further extended to other morphologies.

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2. Experimental section

2.1. Materials. Acrylic acid (AA, Sigma-Aldrich) was dried over anhydrous magnesium sulfate and then distilled under reduced pressure prior to use. Styrene (Sigma-Aldrich) was purified by passing through basic Al2O3 column for removal of the inhibitor prior to use. N,N’Azobis(isobutyronitrile) (AIBN) was purified by recrystallization from ethanol. S-Dodecyl-S’(α,

acid)

α’-dimethyl-α”-acetic

trithiocarbonate

(DDMAT),

trimethylsilyldiazomethane

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(methylation agent) solution 2M in hexane, silver nitrate (AgNO3) and sodium borohydride (NaBH4) were purchased from Sigma-Aldrich and used as received. 2.2. Polymer templates synthesis.

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2.2.1. Synthesis of PAA. A typical synthetic procedure for PAA macro chain transfer agent (PAA-CTA): AA (6.86 mL, 0.1 mol), DDMAT (364 mg, 1 mmol), THF (8.0 mL), and AIBN

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(16.4 mg, 0.1 mmol) with the molar ratio of DDMAT/AA/AIBN=1/100/0.1 were added to a 25 mL Schlenk flask with a magnetic stir-bar. After three freeze-pump-thaw cycles, the flask was sealed and purged with argon, then placed in an oil bath at 70oC while stirring. After reaching a certain conversion, the flask was cooled to room temperature and exposed to air. A yellow product (PAA-CTA1) was obtained by precipitation of the polymerization mixture into excess diethyl ether, followed by filtration and vacuum drying at room temperature overnight. 2.2.2. Synthesis of PAA-b-PS by PISA. The synthetic procedure for block copolymer PAA-bPS1: A dry 50 mL Schlenk flask was charged with PAA-CTA1 (358.5 mg, 0.088 mmol), styrene

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(5 mL, 43.64 mmol), AIBN (1.5 mg, 0.0088 mmol) and 25 mL methanol. Then, the mixture was degassed by three freeze-pump-thaw cycles. Subsequently, the flask was immersed in a thermostated oil bath at 70 oC for certain time. Samples were taken during the polymerization to measure the monomer conversion. Finally, the reaction was stopped by cooling to room

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temperature and exposing to air.

2.3. Synthesis of Ag nanoparticles within the templates: PAA-b-PS@Ag NPs. The PAA-b-PS dispersion was centrifuged at 2000 rpm for 10 min to remove the precipitation of aggregated

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nano-objects, followed by dialysis of the supernatant against water for 2 days to purify the dispersion. Then the solid content of the dispersion was measured prior to further synthetic steps. A typical synthetic protocol for PAA-b-PS3@Ag NPs (Ag+/-COOH=1:3) follows: PAA-b-PS3

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(PAA106-b-PS440) was diluted with water to form 1mg/mL dispersion, the pH was around 4. 116 µL of AgNO3 solution (10 mg/mL in water) was added to the dispersion (Ag+/-COOH=1:3), then NaBH4 (NaBH4/Ag+=2:1), forming a yellow dispersion. The same conditions were used for other samples with the molar ratio of Ag+/-COOH; 1:3, 1:2, 1:1, 2:1 and 3:1. Higher concentrations (5 mg/mL and 10 mg/mL) were also examined. In this paper, the concentrations

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refer to the concentration of the polymer template.

2.4. 1H NMR Characterization. Nuclear magnetic resonance (NMR) was used to determine the conversion during the polymerization. The 1H NMR spectra were recorded on a Bruker Avance

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DPX 250 MHz instrument, using CDCl3 or DMSO-d6 as solvent. 2.5. GPC Characterization. Gel permeation chromatography (GPC) was used to determine the molecular weights and molecular weight distributions. The GPC measurements were carried out

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with a Wyatt instrument equipped with two PSS columns and one guard column, light scattering (LS) and differential refractometer (RI) detectors. The measurements were conducted in DMF with 10 mg/L LiBr as eluent at a flow rate of 1 mL/min. Either linear PS or poly(methyl methacrylate) (PMMA) standards were used for calibration, depending on the polymer composition. PAA-CTA was esterified by (trimethylsilyl)diazomethane, before being injected to GPC, as reported previously.[26] 2.6. TEM Characterization. A 0.01wt % dispersion was dropped on the carbon-coated copper grid and allowed to dry to prepare the sample for TEM. A Jeol 1400 transmission electron

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microscopy (TEM) and Jeol ARM200F HRTEM (High Resolution TEM) were used for the morphology study. 2.7. UV-Vis Characterization. UV-Vis spectra were performed using a Thermo Scientific

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Evolution 220 UV-Vis spectrophotometer with 2 nm resolution. 2.8. SERS Characterization. A triple grating dispersive Raman spectrometer T64000 (JobinYvon) equipped with Olympus B-40 microscope was used to measure the Raman spectra within spectral resolution of c.a. 0.5 cm-1. Radiation of 514.5 nm from argon laser was used for

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excitation with laser power of 0.4 mW, and the acquisition time was 2 × 180 s. The SERS samples were prepared by drop-casting PAA-b-PS@Ag NPs dispersion containing of 200 µM

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adenine onto the chrome substrate.

2.9. Catalytic Characterization. A cuvette was charged with 2.5 mL of NaBH4 (0.01 M) solution and 100 µL of PAA-b-PS2@Ag NPs (Ag+/-COOH=1:1, concentration 1 mg/mL) solution. The calculated mass of Ag NPs was 18 µg, based on the assumed 100% reduction of Ag+ to Ag0. Then 25 µL 4NP (0.01 M) was added to the cuvette. The UV-Vis spectrum was then

3. Results and discussion

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recorded.

The procedure used for the preparation of Ag NPs within the synthesized PISA nano-objects is

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shown in Scheme 1. First, the macro-chain transfer agent (macro-CTA), poly(acrylic acid)-CTA (PAA-CTA), was synthesized by reversible addition-fragmentation chain-transfer (RAFT) polymerization. Next, the macro-CTA was chain-extended by PISA with polystyrene (PS) in

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methanol, forming PAA-b-PS, which after reaching sufficient conversion resulted in formation of the nano-objects. Finally, the nano-objects were used as templates for the synthesis of silver nanoparticles and yielded the hybrid PAA-b-PS@Ag NPs.

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Scheme 1. Synthesis procedure of PAA-b-PS@Ag NPs.

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3.1. Polymer template synthesis.

Macro-CTA with various degrees of polymerization (DP) of PAA in a range of DP=53 to DP=106 were synthesized. GPC results showed that each polymerization was well-controlled providing polymers with low dispersity D<1.2 (values forPAA-CTA were measured after

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methylation). The DP was determined from 1H NMR spectra based on the monomer conversion and confirmed by GPC. All of the polymer compositions, molecular weights and their

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distributions are summarized in Table 1.

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Table 1 Summary of the synthesized macro-CTA, BCPs and formed nano-objects. Mn

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Polymer compositionb

Diameter, PDI

Diameter (TEM)c

(DLS)

PAA-CTA1

8,700 a

1.18

PAA53-CTA

-

-

PAA-CTA2

16,200a

1.19

PAA87-CTA

-

-

PAA-CTA3

18,200a

1.17

PAA106-CTA

-

-

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27,700

1.28

PAA53-b-PS440

65 nm, 0.151

44±2 nm

PAA-b-PS2

44,900

1.34

PAA87-b-PS440

65 nm, 0.082

49±5 nm

PAA-b-PS3

37,000

1.30

PAA106-b-PS440

63 nm, 0.174

55±5 nm

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PAA-b-PS1

the Mn measured after esterification of PAA by (trimethylsilyl)diazomethane

b

the polymer compositions calculated from 1H NMR

c

the diameter of individual bead

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a

The final morphology of PISA objects depends not only on the ratio of two blocks but also on

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the synthetic conditions.[27, 28] The polymerization of styrene from PAA-CTA1 was conducted in methanol, the kinetics is illustrated in Fig.1a. The polymerization started slowly but accelerated due to a higher local concentration of monomer, as reported previously.[1] The dispersity of copolymers formed from presented macro-CTA through PISA did not exceed the value of D= 1.35. The GPC results were consistent with the theoretical molecular weights, which

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confirmed the controlled character of the polymerization.

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Fig. 1. PAA-b-PS1 nano-objects formed by PISA during the polymerization (a) kinetics of

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polymerization; (b) DLS traces recorded at different time intervals, TEM images of nano-objects formed after 27 h (c) and 53 h (d) of polymerization. The PISA process was monitored by measuring the size and morphology of the as-prepared

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dispersions. The gradual growth of the PS solvophobic block from the PAA-CTA changed the solubility of the synthesized block copolymer, which resulted in the spontaneous self-assembly

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and led to the formation of nano-objects. The formation of spherical micelles started after the PS chains reached a certain DP. PS preferentially assembled inside the created micelles, yielding core-shell micelles with a PS core and PAA shell. The outer PAA shell played the role of a stabilizer during the entire chain extension procedure without precipitation of the formed block copolymer. DLS results showed the formation of monomodal nano-objects with average diameter of 40 nm after 27 h (Fig. 1b). The hydrodynamic diameter increased from 40 nm to 65 nm with increasing conversion up to 88 %, which demonstrated the ongoing PISA process. TEM analysis (Fig. 1c) showed the formation of nanospheres with diameter of 25 nm, smaller than the size measured by DLS. This could be due to solvent swelling of the nano-objects. Further size

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increase of the individual beads from 25 nm to 28 nm and then to 44 nm after 29 h and 49 h, respectively was observed for systems with higher DP. Continuation of PISA facilitated the interconnection of the spheres, forming agglomerates of nanospheres and yielding the beadcluster structures with the same primary sphere size (Fig. 1d). The number of spheres within the

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single aggregates ranged randomly from 2 to 10. The spheres tended to aggregate into a string during the ongoing polymerization. Similar morphology, but with different sphere sizes, was observed for PAA-b-PS2 and PAA-b-PS3 (Table 1). Higher order structures such as worm-like and vesicles could be obtained, either by extending the DP of PS chains or by conducting the

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reaction at higher solid content conditions.[14, 29] This report is focused on nano-objects with bead-cluster morphology which served as the well-defined templates for synthesis of silver

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nanoparticles (Ag NPs). The preparation of nano-objects with other morphologies will be reported in the future.

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3.2. Synthesis of Ag nanoparticles within the templates PAA-b-PS@Ag NPs.

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Fig. 2. Ag NPs synthesized within PISA formed templates. (a) UV-Vis spectra of the samples prepared within PAA-b-PS3 with different molar ratios of Ag+/–COOH and different

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concentrations. (b) The size distribution of the in situ formed hybrids using PAA-b-PS3 by DLS. Dark Field Scanning Transmission Electron Microscopy (DF STEM) images of PAA-b-PS@Ag NPs using different templates and varied molar ratio of Ag+/–COOH: (c) PAA-b-PS3, Ag+/–

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COOH = 1:3, (d) PAA-b-PS2, Ag+/–COOH = 1:1, (e) PAA-b-PS3, Ag+/–COOH = 3:1. Carboxylic acid groups, present within the shell of PISA formed bead-cluster micelles. They were used for the preparation of Ag NPs by sequential cation loading employing electrostatic interactions, followed by an in situ reduction. The PAA shell could not only stabilize the Ag NPs but also prevented large agglomeration of Ag NPs.[30] The charge attraction between –COOand Ag+ enabled loading the precursor into the shell of the bead-cluster. Subsequent addition of reducing agent, sodium borohydride (NaBH4), turned the milky dispersion into a yellow one, which indicated the reduction of Ag+ and formation of Ag NPs. Several molar ratios of Ag+ to –

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COOH (Ag+/–COOH =1:3, 1:2, 1:1, 2:1 and 3:1) were used for the preparation of stable Ag NPs. Also, various DP of PAA, and different concentrations of reagents were used. Typical plasmonic spectrum of Ag NPs with absorption peak at 401 nm confirmed the formation

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of Ag NPs in the presence of PAA-b-PS3 (Fig. 2a). The bright dots with diameter of around 5 nm, analyzed by TEM, encompassing the spheres, confirmed the Ag NPs were immobilized on the shell of PAA-b-PS beads, as shown in Fig. 2c, Fig. 2d and Fig. 2e. DLS results showed that the formed nano-objects had the average diameter of 100 nm (Fig. 2b). Their diameter slightly increased in comparison with the pure templates due to further aggregation of primary beads to

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the bead-cluster and the incorporation of Ag NPs. When the molar ratio of Ag+/-COOH was lower than 2, all the Ag NPs were immobilized onto the bead-cluster, no other NPs were

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detected. Increasing molar ratios of Ag+/–COOH resulted in the higher concentration of the Ag NPs, as confirmed by increasing absorption at 401 nm (Fig. 2a). In addition to the main peak at 401 nm, a shoulder peak around 420 nm appeared when the molar ratio of Ag+/–COOH was higher than 2. This peak may be attributed to in situ formation of free Ag NPs outside the template. The excess of reducing agent enabled non-trapped Ag+ to be reduced outside the template to form BH4- stabilized free Ag NPs, with the size of nanoparticles dependent on the

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concentration of BH4- and ratio of Ag+/ BH4-. [31, 32] In contrast to the Ag NPs immobilized within the template, free Ag NPs aggregated to larger size, as confirmed by TEM. Bimodal distribution observed by DLS when the molar ratio of Ag+/–COOH was increased to 2:1 also suggested the co-existence of free Ag NPs with 10 nm diameter and the immobilized ones. The

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free Ag NPs grew from 10 nm to 15 nm when the molar ratio of Ag+/–COOH increased from 2:1 to 3:1. The DLS showed similar size of polymer template within immobilized Ag NPs regardless

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the concentrations used: 1 mg/mL, 5 mg/mL or 10 mg/mL. However, size of free Ag NPs became larger at higher concentrations of the Ag+ and BH4-. Importantly, with a sufficiently high DP of PAA block, the as-prepared dispersions were stable, without any precipitation, even after several months. In contrast, with lower DP of PAA (PAA-b-PS1), precipitation was observed when a higher ratio of Ag+/–COOH was used to prepare the hybrids. The loading amount of Ag NPs showed dependence on the chain length of the stabilizer segments PAA. The longer PAA resulted in the higher amount of immobilized Ag NPs. This was further confirmed by the Dark Field Scanning Transmission Electron Microscopy DF STEM analysis. The homogenous Ag NPs were localized on the shell of the beads for the lower molar ratios of Ag+/–COOH (1:3 to

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1:1) shown in Fig. 2c and Fig. 2d. Larger Ag NPs (around 15 nm) appeared also outside the template in sample with higher molar ratio of Ag+/–COOH (3:1) (Fig. 2e). In a blank experiment, under otherwise the same conditions but in the absence of templating polymer nano-objects, no stable Ag NPs were formed. In summary, the PISA provided a facile method to form uniform

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templates with tuned morphology for Ag NPs synthesis with tailored nanoparticles alignment. The immobilization of Ag NPs on the bead-cluster and the size of in situ formed free Ag NPs can be controlled by the DP of stabilizer within a template, as well as by the variation of the molar

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ratio of Ag+/–COOH. 3.3. Catalytic properties of Ag NPs.

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Ag NPs were evaluated as catalysts for the reduction of p-nitrophenol in the presence of NaBH4 , using the standard UV-Vis spectrophotometric procedure.[33] As shown in Fig. 3, the reduction was followed by the gradual decrease of the intensity of the absorption peak at 400 nm and the increase of the intensity of the absorption peak at 300 nm. The intensity of peak at 400 nm is related to the p-nitrophenol concentration, as shown in inset of Fig. 3. The Ct/C0 was calculated

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from the equations (1):

=

(1)

where C0, Ct and I0, It denote the concentration of p-nitrophenol and intensity of absorption peak

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at 400 nm at the beginning and during the reaction, respectively. Under tested conditions, pnitrophenol was completely reduced to p-aminophenol within 5 min. No reduction was detected for the sample without Ag NPs. That confirmed high catalytic activity of PAA-b-PS2@Ag NPs

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and their accessibility to the p-nitrophenol reagent.

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Fig. 3. UV-Vis spectra of PAA-b-PS2@Ag NPs (Ag+/–COOH=1:1, concentration 1 mg/mL) as catalyst for the reduction of p-nitrophenol in the presence of NaBH4. Inset: the Ct/C0 of 4NP vs

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time.

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3.4. Evaluation of PAA-b-PS@Ag NPs as SERS substrates. Discrete metal nanoparticles (NPs) or their assembled arrays can serve as the hot spots for SERS

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substrates.[34-40] Herein, a layer of Ag NPs within the PISA formed spheres was prepared and tested as a SERS substrate. The efficiency of SERS was evaluated using adenine as a model molecule.

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Fig. 4. (a) Raman spectra of adenine (magenta), PAA-b-PS2 (black) and SERS spectra of PAA-

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b-PS2@Ag NPs (red) and PAA-b-PS2@Ag NPs with adenine (blue). (b) SERS spectra of PAAb-PS2@Ag NPs and PAA-b-PS3@Ag NPs prepared with different molar ratio of Ag+/-COOH. As illustrated in Fig. 4a, spectrum of PAA-b-PS2 shows only the signals typical for polystyrene because Raman spectroscopy is strongly sensitive to non-polar groups. The significant difference between the Raman spectra of PAA-b-PS2 and PAA-b-PS2@Ag NPs indicates interactions

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between polymer templates and Ag NPs. The marked region with high width band of 1100-1700 cm-1, is assigned to stretching vibrations of the carboxylate groups. The doublet within 12001300 cm-1 and triplet within 1490-1600 cm-1 correspond to the symmetric mode and asymmetric mode of carboxylate, respectively. The broad bands and discrete character of the spectrum in this

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range suggested that the -COO- groups of PAA were in different states, which also indicated the involvement of carboxylate anions to the Ag NPs capping.[41] Additionally, the peaks at 817

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cm-1 and 1057 cm-1, marked with asterisks in Fig.4a, are attributed to residual nitrite and nitrate anions, respectively.[42] The PAA-b-PS2@Ag NPs with 0.2 mM adenine showed the featured peaks of adenine at 734, 1319, 1462 and 1589 cm-1.[43] Intensity of these bands was much higher in comparison with analogues peaks in Raman spectrum of 10 mM adenine, confirming the signal enhancement. The aligned Ag NPs on PISA bead-clusters behaved like hot-spots, resulting in the SERS. PAA-b-PS2 and PAA-b-PS3 with different concentrations of Ag NPs were used to verify the SERS signal in detection of 0.2 mM adenine. It was assumed that silver ions introduced into system were fully converted into Ag NPs. The SERS signals were obtained from the samples

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with the molar ratio of Ag+/-COOH < 1. Raman spectrum of 10 mM adenine was used as the reference to calculate the enhancement factor (EF) using the simplified equation (2):[44] (



)/

(

)

(



)/

(

)

(2)

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=

where: Is and IR denote the Raman spectral intensity of peak at 734 cm-1 from SERS substrates and adenine, respectively. Cs(adenine) and CR(adenine) denote the adenine concentration in sample and reference, respectively. As shown in Fig. 4b, the higher enhancement obtained for sample

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with higher Ag NPs concentration (Ag+/-COOH = 3:1), indicates that the EF for adenine depends on the concentration of the Ag NPs. The effect of different chain length of PAA of the template capping the Ag NPs could affect the enhancement factor, since EF of PAA-b-PS2@Ag NPs

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showed higher dependence on Ag NPs concentrations than PAA-b-PS3@Ag NPs. These studies pave the way for fabrication of SERS substrate via PISA. More detailed studies of the effect of templates on SERS and different target molecules are required to enhance the effect and will be

4. Conclusions

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reported in the future.

In summary, a facile approach to prepare hybrid materials of PAA-b-PS@Ag NPs via loading Ag NPs onto a PISA template is reported. PISA of PAA-b-PS block copolymers led to the

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formation of core-shell nano-spheres after the PAA macro-CTA was chain-extended with PS. The size of resulting spheres was related to the molar mass of the formed PS segments. The

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organization of the spheres during polymerization process yielded bead-clusters morphology, depending on the DP of PS. The nanospheres, composed of a PAA shell, served as templates for loading metal ions. A discrete layer of Ag NPs covering bead-clusters was formed by tuning the molar ratio of Ag+/–COOH prior to in situ reduction of the Ag+. Due to self-positioned distribution of Ag NPs on the uniform templates, the as-prepared material facilitated both SERS effect for adenine detection and catalytic activity in the reduction of p-nitrophenol.

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ACKNOWLEDGMENT: We thank for National Science Center, Poland for financial support (via Grant UMO-2014/14/A/ST5/00204). YZ, WR, MK, JP, KK acknowledge the support from National Science Center, Poland (via Grant UMO-2014/14/A/ST5/00204). GH acknowledges the

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Nanoscale and Microscale Research Centre, University of Nottingham for TEM measurements. Authors acknowledge the fruitful discussion with Professors S. Jurga and J. Ulanski.

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Highlights

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PISA process of Styrene with PAA macro-CTA formed bead-clusters morphology They were used as templates to immobilize Ag NPs on the shell of the nano-clusters

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PAA-b-PS@ Ag NPs were used as SERS substrate for adenine detection

PAA-b-PS@ Ag NPs showed excellent catalytic activity in the reduction of

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p-nitrophenol